Cutting of materials can be done mechanically with chisels, knives, scalpels and other tools such as surgical tools. However, prior methods and apparatus of cutting can be less than desirable and provide less than ideal results in at least some instances. For example, at least some prior methods and apparatus for cutting materials such as tissue may provide a somewhat rougher surface than would be ideal. Although lasers having pulse short pulse durations have been proposed to cut tissue, these short pulsed lasers may use very high pulse repetition rates and the energy of these lasers can be difficult to measure in at least some instances. Pulsed lasers can be used to cut one or more of many materials and have been used for laser surgery to cut tissue.
Examples of surgically tissue cutting include cutting the cornea and crystalline lens of the eye. The lens of the eye can be cut to correct a defect of the lens, for example to remove a cataract, and the tissues of the eye can be cut to access the lens. For example the cornea can be cut to access the cataractous lens. The cornea can be cut in order to correct a refractive error of the eye, for example with laser assisted in situ keratomileusis (hereinafter “LASIK”).
Many patients may have visual errors associated with the refractive properties of the eye such as nearsightedness, farsightedness and astigmatism. Astigmatism may occur when the corneal curvature is unequal in two or more directions. Nearsightedness can occur when light focuses before the retina, and farsightedness can occur with light refracted to a focus behind the retina. There are numerous prior surgical approaches for reshaping the cornea, including laser assisted in situ keratomileusis, all laser LASIK, femto LASIK, corneaplasty, astigmatic keratotomy, corneal relaxing incision (hereinafter “CRI”), and Limbal Relaxing Incision (hereinafter “LRI”). Astigmatic Keratotomy, Corneal Relaxing Incision (CRI), and Limbal Relaxing Incision (LRI), corneal incisions are made in a well-defined manner and depth to allow the cornea to change shape to become more spherical.
Cataract extraction is a frequently performed surgical procedure. A cataract is formed by opacification of the crystalline lens of the eye. The cataract scatters light passing through the lens and may perceptibly degrade vision. A cataract can vary in degree from slight to complete opacity. Early in the development of an age-related cataract the power of the lens may increase, causing near-sightedness (myopia). Gradual yellowing and opacification of the lens may reduce the perception of blue colors as those shorter wavelengths are more strongly absorbed and scattered within the cataractous crystalline lens. Cataract formation may often progresses slowly resulting in progressive vision loss.
A cataract treatment may involve replacing the opaque crystalline lens with an artificial intraocular lens (IOL), and an estimated 15 million cataract surgeries per year are performed worldwide. Cataract surgery can be performed using a technique termed phacoemulsification in which an ultrasonic tip with associated irrigation and aspiration ports is used to sculpt the relatively hard nucleus of the lens to facilitate removal through an opening made in the anterior lens capsule. The nucleus of the lens is contained within an outer membrane of the lens that is referred to as the lens capsule. Access to the lens nucleus can be provided by performing an anterior capsulotomy in which a small round hole can be formed in the anterior side of the lens capsule. Access to the lens nucleus can also be provided by performing a manual continuous curvilinear capsulorhexis (CCC) procedure. After removal of the lens nucleus, a synthetic foldable intraocular lens (IOL) can be inserted into the remaining lens capsule of the eye.
Although prior methods and apparatus have been proposed to cut tissue, the fixation of tissue of these prior methods and apparatus can be less than ideal in at least some respects. For example, the prior microkeratomes that have been used to cut corneal tissue with blades can result in less than ideal fixation of the eye, and may provide incomplete or inaccurate cutting of the tissue in at least some instances. Also, at least some of the prior microkeratomes may result in temporary increases in intraocular pressure (hereinafter “IOP”) in at least some instances. Although prior laser systems have been proposed to cut tissue with short laser beam pulses, the methods and apparatus to couple the laser beam to the eye can be less than ideal in at least some instance. For example, at least some of the prior system can result in one or more of increased IOP, incomplete coupling to the eye, or patient movement relative to the laser in at least some instances. Although many patients have been successfully treated with the prior systems, the less than ideal coupling to the patient can result in a somewhat irregular treatment, or an incomplete treatment, for example. Work in relation to embodiments suggests that the coupling of the eye to the laser may be related to variability in the flow of suction to the eye. Also, the feedback provided to the physician can be less than ideal in at least some instances. The less than ideal coupling of the laser to the patient may result in patient movement, or the patient decoupling from the laser system, or both, such that the cutting of tissue may be less than ideal.
Laser based cataract surgery relies on a patient interface device to stabilize the eye to assure proper laser treatment. These interface devices are typically attached to the eye with some type of annular “suction ring” design where a vacuum is applied. If there is a loss of vacuum during laser treatment it is important to shut off delivery of the laser energy before any mistreatment, or even injury, can occur. In most systems the vacuum level is monitored in the instrument at the end of the vacuum supply tube, so that the laser energy is shut off when the vacuum level at that point in the pneumatic circuit drops below a certain level, indicating the patient interface is not in complete suction contact with the eye. This level of monitoring may not react quickly enough in certain cases, in particular where fluid is present as an optical medium from the laser to the cornea.
Thus, improved methods and apparatus to couple patients to treatment devices such as lasers would be helpful.